Polyethylene (HDPE or LDPE) will not adhere to fluoropolymers, e.g. a VDF (vinylidene fluoride) homopolymer (PVDF) or a copolymer of VDF with hexafluoropropylene (HFP), without a tie layer.
Matsumoto et al. U.S. Pat. Nos. 4,410,595, issued Oct. 18, 1983, and 4,423,185, issued Dec. 27, 1983, disclose thermoplastic resinous compositions, sheets of which are useful for creating laminates with sheets of a wide variety of other materials, most of which are polymer resins.
More particularly, the thermoplastic resinous compositions of the above patents are taught to consist essentially of (a) 5 to 70% by weight of a thermoplastic polyurethane elastomer, and (b) 30 to 95% by weight of a modified polyolefin or olefin copolymer, having functional groups of at least one type selected from the group consisting of a carboxyl group, a carboxylate group, a carboxylic anhydride group, an amide group, a hydroxyl group and an epoxy group.
The other materials to which these compositions can be adhered in laminar form are taught to comprise at least one material selected from the group consisting of vinyl chloride polymer resins, thermoplastic polyester resins, ethylene/vinyl alcohol copolymer resins, polyamide resins, polyacrylonitrile and nitrile copolymer resins comprising at least 50% by weight of units derived from an unsaturated nitrile, polystyrene and styrene copolymer resins, polymethyl methacrylate and acrylic or methacrylic acid ester copolymer resins, polyurethane resins, olefin polymer resins, polyacetal resins, polyvinyl acetal resins, polycarbonate resins, polyphenylene oxide resins, polysulfone resins, epoxy resins, phenol-formaldehyde resins, unsaturated polyester resins, melamine-formaldehyde resins, urea-formaldehyde resins, synthetic rubbers, paper, wood and other cellulosic materials, cements, glass and other ceramic materials and metals.
These patents do not indicate that fluoropolymers can be laminated with the thermoplastic compositions of their invention. This is significant because the difficulty of bonding fluoropolymers to other surfaces is well known. Further, while these references teach that the backbone chains of their thermoplastic polymer resins, including polyurethanes, comprise ester linkages, they do not distinguish between aliphatic polyester-based polymers and non-aliphatic polyester-based polymers.
U.S. Pat. Nos. 4,221,757 and 4,291,099, issued to A. Strassel on Sep. 9, 1980 and Sep. 22, 1981, respectively, relate to laminates of polyvinylidene fluoride resin and a thermoplastic polyurethane, which laminates are formed without the use of any intermediate bonding agent. The bonding is preferably effected by coextrusion, which requires the polyvinylidene fluoride to have a specified apparent viscosity at 200.degree. C., at specified velocity gradients. The polyvinylidene flouride resins may be homopolymers of vinylidene fluoride or copolymers containing at least 70% by weight of vinylidene fluoride.
The thermoplastic polyurethanes to which the polyvinylidene fluorides are laminated are disclosed to be linear or only slightly cross-linked polyurethanes obtained "by the known and conventional reaction of an organic diisocyanate with a diol, polyether and/or polyester having a molecular weight falling between 500 and 6000 . . . . " Useful diols, polyethers and polyesters for forming these polyurethanes are disclosed to include polyols, polyethers and polyesters copolymerized or grafted with acrylonitrile, acrylonitrile/styrene, methyl styrene, vinyl chloride, vinylidene chloride or methyl methacrylate. While other polymers may be blended with the polyurethane, these patents do not teach the use of an intermediate bonding layer between the polyvinylidene fluoride layer and the polyurethane layer, nor do they teach further laminating other materials to the polyurethane/polyvinylidene fluoride laminates.